Size and shape dependences of the colloidal silver nanoparticles on the light sources in photo-mediated citrate reduction technique

Colloidal silver nanoparticles (Ag NPs) with different sizes and shapes were synthesized by photo-mediated citrate reduction of aqueous $$\hbox {AgNO}₃$$ solution under UV, sun and visible–infrared (VIS–IR) light sources. Pale yellow colour colloid was obtained under VIS–IR light exposure, whereas reddish yellow colour colloid was yielded under UV light. The colloid prepared under natural sunlight initially appeared as yellow, which turns out to be deep green after 10 h exposure. The colloid prepared under UV light contains fine spherical NPs with diameter ranging from 5 to 10 nm. In addition to spherical NPs, some low-dimensional features like triangles, hexagonal platelets, nanorods were also formed under sunlight. Similar low-dimensional features including spherical particles, long chains of particles and large leaf-like platelets were grown under VIS–IR light. The colloid prepared under UV light exhibits single plasmonic absorption peak in the violet region of the visible spectra with absorption peak centred at $${\sim }405$$ nm. However, the colloid prepared under sun and VIS–IR light demonstrates multiple plasmonic absorption peaks related to the multi-dimensional nanoparticles. All the NPs were made of pure silver and single crystalline. The colloid prepared under VIS–IR light exhibited significant ageing with time; whereas, the colloids prepared under UV and sunlight seem very stable against ageing even after long time.